I originally came across this
thread by googling the permies site for questions using the search term "how many chickens". I am doing some calculations right now trying to figure out exactly how many chickens one would need to be self-sustaining. I could not find a good answer on google or on the permies website, so I decided to do some investigating and figure out the math myself. Everyone is going to have different facts about their different breeds, and I have absolutely no
experience raising chickens; however, I am highly skilled in mathematics having done my masters degree in computer science so I'd still say my two cents is worthwhile advice (especially since I've taken my facts from chicken raising expert sources). I'm going to share my calculations, but keep in mind I am leaning very conservatively in my calculations. Most people should produce MORE chickens than estimated, but some will inevitably produce less because of unexpected consequences. Let's start by laying out the ASSUMED numbers and the facts.
1. Chickens lay about 2 eggs per 3 hens twice a week on worst case average. Again, I'm being VERY conservative (because some people would see this as absurd with their breed). This comes out to 1 chicken producing about 1 and 1/3 an egg every week.
2. A family of 4 eats about 2 chickens a week (some say 1 chicken, I'm being conservative and saying 2 chickens because I know my family eats at least 2 chickens a week and I only have 3 people in my family).
3. You can mate about 10 hens to 1 rooster (again an arguable number but this is the one I chose to use).
4. It takes about 1 month for an egg to develop into a chick (incubation can take as early as 21 days I've read, but again we're being conservative).
5. It takes about 6 months for a hen to fully develop and start laying eggs.
6. Eggs have a poor incubation rate of about 25% success on average (meaning only 25% of eggs incubated turn into baby chicks).
Okay, so now we have some numbers to work with. Now let's do some math. Let's assume we want to go off grid next week. We need to answer the serious question:
How many hens/roosters do we need to purchase up front to ensure for the next year (52 weeks) our family will have enough chicken to eat?
At first I thought you would need to buy at least 52 chickens if you wanted to start eating and breeding right away because you would need to slaughter at least 52 in the 6-7 months in order to have chicken to eat while the little ones were raised. Now that I actually am writing about this problem of self-sustaining chickens, it seems it would be easier to buy chicken from the market until you could build up a self-sustaining population. Therefore I will assume for the rest of the calculations we need to figure out how many chickens we need to raise 7 months from now (1 month for eggs to hatch, 6 months for bird to develop) in order to sustain our chicken population to slaughter for food and then go from there.
So I am going to start by looking at the finish. We need to produce 104 chickens a year (2 chickens a week) to slaughter for food. Thus the calculation is becoming simpler. Now, seemingly, the only question we need to answer is "How many eggs will it take to produce 52 chickens in 7 months"? And we'll round 7 months to 6 months just to make the estimating easier (because we've been so conservative with our numbers). However, it's more difficult than that because we're slaughtering our breeders as well and a chicken can lay an egg that can hatch at a later time period than the ones we are going to eat. I have no idea what the successful fertilization rates are for roosters mating hens, but we do know about 1/4 eggs hatch when incubated so we know if we incubated 208 eggs about 52 of them would turn out to be chickens in 6 months. In order to lay 208 eggs we would need about 157 hens to each lay us an egg in 1 week (seems strange but 208 eggs divided by hens laying 1 1/3 eggs on average a week comes out to be 157 hens). Over the period of 6 months, the hens would lay many many more half year supplies of eggs thought if we started with 157 hens at week 1, so now our question gets even narrower. The question now becomes "How many chickens does one chicken need to produce over it's lifespan before I can slaughter it for food?"
If we take the 1 1/3 egg per hen metric, let's say in 3 weeks we will get 4 eggs from 1 hen. Let's say over 6 months we will get (4 eggs x 18 weeks =) 32 eggs. With a little luck, 1/4th of them will hatch and we will get 8 chickens over the 6th month span before we slaughter the hen. Wouldn't it be great to get 8 chickens for 1 chicken we raised over a 6 month period? It would be, but I am very skeptical about the theoretical numbers I am coming up with on this. At least we are closer to the answer that 1 hen could produce about 8 hens in 6,7,8,9,10,11,12,13,14ish months. I bet in reality though, 1 chicken probably produces closer to 2-4 chicks per 6 months. What this means is that in order to meet 104 chickens a year, we really only need about 26 breeder chickens in our flock at any time just for breeding. After we're done with the breeding we can slaughter them because they will have produced enough for the next 6 months. Thus about 3 or 4 roosters and 26 hens would be sustainable.
I know my math doesn't exactly make 100% sense, but this is all the time I have to ponder about it and it seems to be in line with all the other forums I've looked at. I may revisit this post after I read up more or want to crunch out the numbers again. I felt it still constructive to post this unfinished, first draft, unrevised post about self-sustaining chickens. Thank you for not being too critical of me, but please feel free to add any math or opinions.